JP2012169866A - Image processing apparatus, image processing method and image processing program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing apparatus, an image processing method and an image processing program capable of performing color management simply and appropriately for an image formation medium whose color reproduction characteristics are unknown.SOLUTION: A color image processing apparatus comprises: a PCS → CMYK conversion part 6; a sheet register list 35 in which multiple sheet profiles are associated with multiple registered sheets to be registered; profile management means 13 which extracts based on a characteristic amount calculated from spectrum reflection characteristics of a user sheet set in an image forming apparatus 42 a registered sheet which can be approximated to color reproduction characteristics of a user sheet from among the multiple registered sheets registered in the sheet register list 35; a management setting screen which accepts user operation instructing the profile management means 13 to extract the registered sheet which can be approximated to the color reproduction characteristics of the user sheet as well as presenting a user the registered sheet extracted by the profile management means 13.

Description

  The present invention relates to an image processing apparatus, an image processing method, and an image processing program for performing image processing for unifying reproduction colors in an image forming apparatus that forms a color image on an image forming medium by superimposing a plurality of basic colors. About.

  For an image forming apparatus that forms a color image on an image forming medium based on basic color digital data such as CMYK, such as a color printer, color copier, or color printer, the input data is reproduced. In order to unify the colors, image processing called color management is performed. As this color management, a color management framework proposed by the ICC (International Color Consortium) and an ICC profile which is a data format are widely known.

  As is the case with ICC profiles, in many of the color management of printing systems with strong nonlinearity, a multidimensional LUT (Look Up Table) that associates the input color space with the output color space, and CMYK that linearizes the input and output of these. The basic unit of conversion is configured by a combination of one-dimensional LUTs for each color channel. The one-dimensional LUT of the input / output channel at this time is called a TRC in the meaning of a tone reproduction curve or tone response correction. Note that the TRC does not necessarily have to be mounted as an LUT, but in many cases, the TRC is mounted as an LUT for ease of mounting and versatility.

  In the case of the ICC framework, as such color conversion, a method that mediates a device-independent color space called PCS (Profile Connection Space), and direct mapping between the TRC of the input / output channels and the multidimensional LUT without using the PCS. A method (called device link) is provided. In the ICC, a color space of the CIE 1976 Lab color system, the CIE 1931 XYZ color system, or a partial space thereof is used as the PCS. In the following description, data holding a multi-dimensional LUT for performing color conversion between the input / output channel TRC and the channel as described above is not limited to the ICC, and is referred to as a color profile or simply a profile (this specification). According to the definition in the document, the ICC profile format is a package of a plurality of profiles according to the rendering intent and the conversion direction.)

  In the color management framework as described above, an image forming apparatus that supports a plurality of types of printing paper or a plurality of types of media (image forming media) requires different color profiles for media having different color reproduction characteristics. Become. Furthermore, even for the same media, multiple profiles that are adjusted for printing conditions such as the number of dotted lines, content types such as text, graphics, and photographs, or color gamut compression intentions are required. The number of necessary profiles tends to increase for customer demands to support various media. For this reason, it is difficult in terms of cost and management to provide a profile that meets all media and output conditions on the maker side that provides the image forming apparatus. Therefore, the manufacturer provides profiles only for some typical media and output conditions, and entrusts the user to create profiles for the rest.

  However, in profile creation, it is relatively easy to construct a color reproduction model that is a mapping from the device color space to the PCS, whereas the device color space (CMYK in many image forming apparatuses) Mapping to a parameter space) involves an unstable process that maps out-of-gamut colors that are not reproducible to the device to colors in the gamut that can be reproduced, so technically prone to unexpected defects in the constructed mapping With great difficulty. Such a mapping defect is likely to occur in an adjustment that adds “preferability” to the reproduced color, and is an element that requires a certain degree of experience.

  For the problem of increasing the number of profiles corresponding to various media as described above, for example, a conventional technique described in Patent Document 1 has been proposed. Japanese Patent Application Laid-Open No. 2005-228561 describes an image forming medium with an unknown color reproduction characteristic that is used by a user to output an image from a plurality of standard sheets that are preset image forming media with known color reproduction characteristics. The idea of selecting a sheet that approximates a user sheet and synthesizing conversion data of image data based on the color reproduction characteristics of the selected sheet is disclosed.

  However, the technique described in Patent Document 1 is a technique for generating conversion data for device link type RGB → CMYK conversion for user paper, and this conversion data is the same standard paper as RGB → CMYK conversion for standard paper. Are combined by CMYK → PCS conversion for user and PCS → CMYK conversion for user paper. Therefore, it is indispensable to separately obtain a profile relating to user paper, particularly PCS → CMYK conversion that requires experience in the generation described above, and the difficulties associated with profile construction by the user are not essentially solved. Become.

  Further, in Patent Document 1, as a specific method for selecting a standard sheet that approximates a user sheet, (a) designation by a user, (b) determination from process parameters such as fixing parameters, and (c) generated from a user sheet. Judging from the profile, three methods are suggested.

  However, in the method (a) above, when the user himself / herself does not know which of the plurality of preset standard papers is the paper that approximates the user paper, the user paper is approximated. There is a problem that standard paper cannot be selected.

  In the method (b), the process parameter is usually determined as a physically printable condition (such as a condition that allows transfer / fixing to be performed normally and does not cause a paper jam). Therefore, there is a problem that it is difficult to obtain sufficient classification performance for use in classification relating to color reproduction characteristics.

  In the method (c), the color reproduction characteristics of a plurality of standard papers and user papers can be directly compared, so that it is possible to determine a desired paper type from the viewpoint of color reproduction. However, in order to select a standard paper that approximates the user paper by the method (c), a determination profile is required prior to the determination, and thus the above-described difficulty in profile creation cannot be avoided. There's a problem. Further, since the paper type cannot be determined until the profile is created, the necessity of profile creation cannot be determined prior to profile creation. For this reason, a burden that the user has to create a profile that does not need to be created is generated. In addition, in order to select an existing profile of standard paper that approximates the user paper, it is necessary to calculate the correlation with all existing profiles, so if the number of registered standard paper profiles is enormous, select There arises a problem that the processing load (processing time) for calculation becomes too large.

  In Patent Document 2, a paper type detection unit is provided on the image output terminal side, and the detected paper type is transmitted to the host PC. The host PC converts the reference color conversion from the reference color conversion table storage unit according to the paper type. A method is disclosed in which a table is selected, an applied color conversion table is generated from a reference color conversion table, and image data is converted using the applied color conversion table.

  In this case, since the paper type can be determined prior to the drawing process of the image output terminal, there is an advantage that the paper determination information can be used for the subsequent applied color conversion table generation determination. However, the paper type detection unit disclosed in Patent Document 2 is a determination method based on reflected light and transmitted light of a paper, and is not a multidimensional determination method based on a spectral wavelength. There arises a problem that the type cannot be determined sufficiently.

  The present invention has been made in view of the above, and provides an image processing apparatus, an image processing method, and an image processing program capable of simply and appropriately performing color management on an image forming medium whose color reproduction characteristics are unknown. The purpose is to do.

  In order to solve the above-described problems and achieve the object, the image processing apparatus according to the present invention unifies reproduction colors in an image forming apparatus that forms a color image on an image forming medium by superimposing a plurality of basic colors. An image processing apparatus for performing image processing to achieve color processing, and based on registered color conversion parameters, a color value that depends on another device different from the image forming apparatus, or a color that does not depend on the device A color conversion means for converting the value into a color value corresponding to each basic color of the image forming apparatus; a registration list in which the plurality of color conversion parameters are registered in association with a plurality of image forming media having different color reproduction characteristics; A plurality of image forming media registered in the registration list based on a feature amount calculated from a spectral reflection characteristic of a use medium that is an image forming medium set in the image forming apparatus. Parameter management means having a function of extracting an image forming medium that can approximate the color reproduction characteristics of the used medium, and instructing the parameter management means to extract an image forming medium that can approximate the color reproduction characteristics of the used medium And a user interface for presenting the image forming medium extracted by the parameter management means to the user.

  An image processing method according to the present invention is an image processing apparatus for unifying reproduction colors in an image forming apparatus that forms a color image on an image forming medium by superimposing a plurality of basic colors. Based on the color conversion parameters that are used, a color value that depends on another device that is different from the image forming apparatus or a color value that does not depend on the device is represented by a color corresponding to each basic color of the image forming apparatus. An image processing method executed in an image processing apparatus comprising: a color conversion unit that converts a value into a value; and a registration list in which a plurality of color conversion parameters are registered in association with a plurality of image forming media having different color reproduction characteristics. Among the plurality of image forming media registered in the registration list, an image forming medium capable of approximating the color reproduction characteristics of a used medium that is an image forming medium set in the image forming apparatus A step of accepting a user operation for instructing extraction, and color reproduction characteristics of the used medium among a plurality of image forming media registered in the registration list based on a feature amount calculated from a spectral reflection characteristic of the used medium And an image forming medium that can be approximated to each other, and a step of presenting the extracted image forming medium to a user.

  An image processing program according to the present invention is an image processing apparatus for unifying reproduction colors in an image forming apparatus that forms a color image on an image forming medium by superimposing a plurality of basic colors. Based on the color conversion parameters that are used, a color value that depends on another device that is different from the image forming apparatus or a color value that does not depend on the device is represented by a color corresponding to each basic color of the image forming apparatus. Set in the image forming apparatus, an image processing apparatus comprising color conversion means for converting to a value and a registration list in which a plurality of color conversion parameters are registered in association with a plurality of image forming media having different color reproduction characteristics. Based on the feature amount calculated from the spectral reflection characteristics of the used medium that is the image forming medium, color reproduction of the used medium among the plurality of image forming media registered in the registration list Characterized in that to realize the function of extracting an image forming medium that can approximate the sex.

  According to the present invention, when an image forming medium with unknown color reproduction characteristics is set in the image forming apparatus and a color image is formed, a plurality of items registered in the registration list in accordance with a user instruction received by the user interface. Image forming media that can approximate the color reproduction characteristics of the image forming medium set in the image forming apparatus are extracted from the image forming medium. There exists an effect that it can implement simply and appropriately.

FIG. 1 is a configuration diagram of an image forming system including a color image forming apparatus. FIG. 2 is a configuration diagram illustrating an outline of the image forming apparatus. FIG. 3 is a functional block diagram showing an outline of an image processing process in the color image processing apparatus. FIG. 4 is a diagram illustrating an example of a paper registration list used by the profile management unit of the color image processing apparatus. FIG. 5 is a diagram illustrating an example of a color management setting screen displayed as a user interface on the console of the color image processing apparatus. FIG. 6 is a diagram illustrating an example of a paper profile setting screen displayed when the new / edit menu is selected in the color management setting screen of FIG. FIG. 7 is a flowchart showing a flow of color management setting processing executed by the profile management unit in response to a user operation using the color management setting screen of FIG. FIG. 8 is a flowchart showing details of the sheet estimation processing in step S103 of FIG. FIG. 9 is a diagram showing the average spectral reflectance experimentally obtained from a representative paper sample group. FIG. 10 is a diagram showing principal component vectors of the paper sample group in FIG. FIG. 11 is a diagram illustrating score distributions of the first principal component and the second principal component of the paper included in the paper sample group in FIG. 9. FIG. 12 is a flowchart showing details of the calibration process in step S109 of FIG. FIG. 13 is a conceptual diagram illustrating a method for generating a sheet correction TRC that minimizes an error evaluation value with respect to a sheet characteristic for a sheet profile.

  Exemplary embodiments of an image processing apparatus, an image processing method, and an image processing program according to the present invention are explained in detail below with reference to the accompanying drawings.

  FIG. 1 is a configuration diagram of an image forming system including a color image processing apparatus according to the present embodiment. The color image processing apparatus 41 according to the present embodiment is realized by a control PC and expansion hardware and control software installed in the control PC.

  Connected to the color image processing apparatus 41 is an image forming apparatus 42 that forms an image on a sheet, which is a physical image forming medium, based on image data processed by the color image processing apparatus 41. The image forming apparatus 42 uses four colors of cyan (C), magenta (M), yellow (Y), and black (K) as basic color materials, and forms a full-color image on a sheet by using these mixed colors.

  On the other hand, the color image processing apparatus 41 is connected to the network 43, receives image data (original data) sent from the user PC 40 connected to the same network 43, and performs an image processing process to be described later. The image is transferred to the image forming apparatus 42.

  Further, the color image processing device 41 is connected to the color measuring means 12 used for calibration of the image forming device 42 and measurement of color reproduction characteristics. A spectrocolorimeter is used as the colorimetric means 12, but a tristimulus value direct-reading colorimetric device can be substituted in a simpler configuration.

  FIG. 2 is a configuration diagram showing an outline of the image forming apparatus 42. The image forming apparatus 42 includes image forming units 90c, 90m, 90y, and 90k corresponding to four colors of cyan (C), magenta (M), yellow (Y), and black (K). These image forming units 90c, 90m, 90y, and 90k are based on the image data transferred from the color image processing device 41, and each color of cyan (C), magenta (M), yellow (Y), and black (K). Create a toner image. The toner images formed by these image forming units 90c, 90m, 90y, and 90k are superimposed on the intermediate transfer belt 91 that circulates in the direction indicated by the arrow in the drawing, so that the color is formed on the intermediate transfer belt 91. The toner image is formed.

  On the other hand, sheets to be printed are accumulated in sheet feed stackers (medium storage units) 94 a and 94 b, picked up one by one from the sheet feed stacker selected by the color image processing device 41, and a sheet transport path 96. It is conveyed along. When the toner image formed on the intermediate transfer belt 91 reaches the position of the transfer roller portion 92, the transfer roller portion 92 transfers the toner image onto the paper transported along the paper transport path 96, and then fixes the toner image. Heat fixing is performed by the device 93. Then, the paper on which the toner image has been fixed is discharged to a paper discharge stacker 95.

  Further, the sheet feeding stackers 94a and 94b for accumulating sheets are provided with spectral colorimetry devices (medium sensors) 97a and 97b, respectively. These spectral colorimetric devices 97a and 97b measure the surface of the uppermost paper stored in the paper feed stackers 94a and 94b in response to a request from the color image processing device 41 to obtain a spectral reflectance (spectral reflection characteristic). Is detected and returned to the color image processing apparatus 41.

  FIG. 3 is a functional block diagram showing an outline of an image processing process in the color image processing apparatus 41. The outline of the image processing process in the color image processing apparatus 41 will be described below with reference to FIG.

  Original data 1 input to the color image forming apparatus 42 is first developed by a RIP (Raster Image Processor) 2 into a bitmap in which attribute information is added to color signals for each pixel of RGB or CMYK. Here, as the attribute information, information such as which object of the character, photograph, or graphics the pixel belongs to is given. Many of the processing parameters after RIP2 are switched depending on this attribute information. Since the processing is performed on a pixel basis, the portion related to object switching is omitted in FIG. 3 for the sake of simplicity. However, in the case of software implementation, the processing from the color management module 3 to the gradation processing means 9 may be branched according to the attribute information, and in the case of hardware implementation, the gradation management means from the color management module 3 having different settings. By performing a plurality of processes up to 9 in parallel and selecting a signal at the entrance to the image forming apparatus 42 according to the attribute information, switching for each object is realized.

  The subsequent color management module 3 converts the device-dependent color space values such as RGB and CMYK into values of the CMYK color space, which is the basic color of the image forming apparatus 42, via the PCS, which is a device-independent color space. To do. As the PCS, CIE1976Lab, CIE1931XYZ, or a partial space thereof is usually used. In the present embodiment, a media relative Lab value with white paper as a white reference is assumed as the PCS, but the device-independent color space to be mounted is not necessarily limited to this.

  The color management module 3 mainly includes an RGB → PCS conversion unit 4 that converts an RGB signal into a PCS signal, a CMYK → PCS conversion unit 5 that converts a CMYK signal into a PCS signal, and a PCS signal into a CMYK signal. The PCS → CMYK conversion unit 6 to be converted is composed of each conversion element. Prior to processing, the above-described color profile, which is a color conversion parameter necessary for conversion, is set for these conversion elements. These color profiles are stored in the following database (DB) associated with each conversion element.

  The simulation profile DB 14 holds color conversion parameters (hereinafter referred to as simulation profiles) for the RGB → PCS conversion unit 4 and the CMYK → PCS conversion unit 5. Prior to processing in the RGB → PCS conversion unit 4 and the CMYK → PCS conversion unit 5, simulations of the RGB → PCS conversion unit 4 and the CMYK → PCS conversion unit 5 are performed according to the setting of a user interface described later displayed on the console 18. A profile is read from the simulation profile DB 14 and set. However, when the profile is originally embedded in the document data 1, the embedded profile is used depending on the setting of the user interface displayed on the console 18 (when the check box 32 shown in FIG. 5 is ON). .

  The paper profile DB 15 holds color conversion parameters (hereinafter referred to as a paper profile) for the PCS → CMYK conversion unit 6. Prior to the processing in the PCS → CMYK conversion unit 6, the paper profile selected from the paper profile DB 15 according to the setting of the user interface displayed on the console 18 or the automatic determination by the calibration described later is the PCS → CMYK. It is set in the conversion unit 6. As a result, the PCS → CMYK conversion unit 6 converts the Lab value on the PCS into a CMYK value that substantially matches the reproduced color Lab reproduced as the output image 11 in accordance with the processing after the paper correspondence correction unit 7.

  Both the paper correspondence correction unit 7 and the gradation correction unit 8 correct gradation characteristics using a one-dimensional LUT (TRC) provided for each channel of C, M, Y, and K colors. Here, the TRC used in the paper correspondence correction unit 7 is a gradation correction parameter (hereinafter referred to as paper correction TRC) used for the purpose of relaxing the difference in color reproduction characteristics for each paper supported by the image forming apparatus 42. And registered in the sheet correction TRC-DB 16. The TRC used in the gradation correction unit 8 is a gradation correction parameter (hereinafter referred to as gradation correction data) used for the purpose of absorbing the characteristic difference of gradation processing set in the gradation processing unit 9. And is registered in the gradation processing parameter DB 17 in association with the gradation processing parameters set in the gradation processing means 9.

  In accordance with the set gradation processing parameters, the gradation processing means 9 configures a halftone dot (area modulation) by combining a plurality of pixels with the output value of the gradation correction means 8 for each color of 8 bits, so that 1 pixel is 2 bits. It is converted into input data of the image forming apparatus 42.

  The gradation processing parameter DB 17 maintains a set of gradation processing parameters for each color set in the gradation processing means 9 and gradation correction data set in the gradation correction means 8 that is a combination thereof. Prior to the processing by the gradation processing means 9 and the gradation correction means 8, a set of gradation processing parameters and gradation correction data is read from the gradation processing parameter DB 17 in accordance with the settings of the user interface displayed on the console 18. Then, gradation processing parameters are set in the gradation processing means 9 and gradation correction data are set in the gradation correction means 8, respectively.

  The profile management means 13 manages and sets profiles and TRCs held in each database according to the settings of the user interface displayed on the console 18. In particular, the profile management means 13 has a function that allows color management to be easily performed using a paper registration list 35 as shown in FIG. Specifically, the profile management unit 13 has a functional configuration that operates when a setting sheet estimation button 33 is pressed on a color management setting screen 20 (see FIG. 5) described later displayed on the console 18 as a user interface. , Spectral reflectance acquisition means 13a, calculation means 13b, and extraction means 13c. The profile management unit 13 has a functional configuration that operates when a calibration execution button 22 is pressed on a color management setting screen 20 described later, and includes a calibration chart output control unit 13d, a colorimetric value acquisition unit 13e, and a classification unit. 13f, determination means 13g, selection means 13h, and generation means 13i.

  In the paper registration list 35, as shown in FIG. 4, a score value, which is a characteristic value reflecting the color reproduction characteristics of paper that has already been registered, an entry (prof.id) in the paper profile DB 15, and a paper correction TRC- An entry (TRC) in the DB 16 is described in association with each sheet. Note that a standard registration area 36 and a user registration area 37 are provided in the paper registration list 35, and information on standard paper registered in advance is held in the standard registration area 36, and user paper ( Information relating to a sheet (optionally used by the user) is held in the user registration area 37. The score value is a value calculated based on the spectral reflectance of the paper, as will be described later.

  The entry of the sheet profile DB 15 corresponds to a reference sheet that represents a sheet group supported by the image forming apparatus 42 in advance (a standard sheet whose information is stored in the standard registration area 36 in the sheet registration list 35 of FIG. 4). The paper profile to be registered is registered. These paper groups roughly include classifications such as glossy paper, matte paper, and plain paper, but in reality these classifications do not necessarily match the color reproduction characteristics, so the classification is the actual color of each paper. Perform based on reproduction characteristics. When a paper profile corresponding to the user paper is generated by calibration for the user paper, the paper profile corresponding to the user paper is also registered in the entry of the paper profile DB 15.

  The spectral reflectance acquisition unit 13a supplies paper to the spectral colorimetric devices 97a and 97b provided in the image forming apparatus 42 when the setting paper estimation button 33 is pressed on the color management setting screen 20 described later. It is required to detect the spectral reflectance of the paper accumulated in the stackers 94a and 94b (corresponding to the “used medium” described in the claims), and the spectral of the paper detected by the spectral colorimetry devices 97a and 97b. Get reflectance. Here, the setting paper estimation button 33 is pressed on the color management setting screen 20 described later when the user paper whose color reproduction characteristics are unknown is used as an image forming medium. The spectral reflectance of the user paper (used medium) with unknown color reproduction characteristics detected by the spectral colorimetry devices 97a and 97b is acquired. In consideration of the case where user paper is accumulated only in one of the paper feed stackers 94a and 94b, for example, the user selects a paper feed stacker to be used by a user interface different from the color management setting screen 20. In other words, it is desirable that the spectral reflectance acquisition unit 13a acquires a detection value from the spectral colorimetry device corresponding to the selected paper feed stacker.

  Based on the spectral reflectance of the user paper acquired by the spectral reflectance acquisition means 13a, the calculating unit 13b reflects the feature amount reflecting the color reproduction characteristics of the user paper, specifically, the third principal component of the user paper. The score values (s1, s2, s3) representing the principal component scores of are calculated. Since the principal component score calculation method is a widely known technique, detailed description thereof is omitted here.

  The extracting unit 13c compares the score values of the user paper calculated by the calculating unit 13b with the score values of the already registered papers (hereinafter referred to as registered papers) described in the paper registration list 35. The difference evaluation value of is obtained. Then, the extracting unit 13c estimates a paper whose difference evaluation value with respect to the score value of the user paper is equal to or less than a predetermined threshold among a plurality of registered papers as a paper having a color reproduction characteristic similar to the user paper, which will be described later. The registered list 29 displayed when the pull-down menu 21 is pressed on the color management setting screen 20 is limited to registered sheets whose difference evaluation value with respect to the score value of the user sheet is equal to or less than a predetermined threshold. In other words, the extraction unit 13c extracts paper that can approximate the color reproduction characteristics of the user paper (used medium) set in the image forming apparatus 42 from the registered paper in response to pressing of the setting paper estimation button 33. As a result, the sheets displayed in the registered list 29 are narrowed down. When an arbitrary sheet is designated by the user from the registered list 29, a sheet profile corresponding to the sheet designated by the user is read from the sheet profile DB 15 and the PCS of the color management module 3 → It is set in the CMYK conversion unit 6. As a result, the PCS → CMYK conversion unit 6 of the color management module 3 uses the paper profile corresponding to the paper designated by the user among the registered papers that are estimated to have similar color reproduction characteristics to the user paper. Are converted into CMYK signals.

  The calibration chart output control means 13d sends test image data (patch image data) to the gradation correction means 8 when the calibration execution button 22 is pressed on the color management setting screen 20 described later, and the image forming apparatus 42. Output from. The output image 11 of the image forming apparatus 42 at this time is a calibration chart in which a plurality of single-color and mixed-color patch images are formed on user paper (use medium) whose color reproduction characteristics are unknown. That is, the calibration chart output control unit 13d performs processing for outputting the calibration chart to the image forming apparatus 42 during calibration. The calibration chart output from the image forming apparatus 42 is measured by the color measuring unit 12 in accordance with a user operation.

  The colorimetric value acquisition unit 13e acquires the colorimetric value obtained by measuring the color of the calibration chart from the colorimetric unit 12.

  The classifying unit 13f classifies the plurality of registered sheets registered in the sheet registration list 35 into a plurality of groups (sheet types) based on the above-described score value of each registered sheet.

  Based on the score value of the user paper calculated by the calculation means 13b, the determination means 13g determines which of the plurality of groups (paper types) the user paper belongs to is classified by the classification means 13f.

  The selecting unit 13h measures the number of registered papers that belong to the same group as the user paper among the plurality of registered papers registered in the paper registration list 35, that is, registered paper of the same paper type as the user paper. A registered sheet having a color reproduction characteristic closest to the characteristic of the colorimetric value acquired by the color value acquisition unit 13e is selected.

  The profile management unit 13 reads a sheet profile corresponding to the registered sheet selected by the selection unit 13 h from the sheet profile DB 15 and sets it in the PCS → CMYK conversion unit 6 of the color management module 3. Thus, the PCS → CMYK conversion unit 6 of the color management module 3 converts the PCS signal into a CMYK signal using the paper profile corresponding to the registered paper selected by the selection unit 13h.

  The generation unit 13i generates a sheet correction TRC that is a gradation correction parameter for correcting a difference in color reproduction characteristics between the registered sheet selected by the selection unit 13h and the user sheet. That is, when the PCS → CMYK conversion unit 6 of the color management module 3 performs color conversion using the sheet profile corresponding to the registered sheet selected by the selection unit 13h, the generation unit 13i performs this PCS → CMYK conversion. A paper correction TRC for each color of C, M, Y, and K is newly generated for performing gradation correction that optimizes the output color reproduction characteristics in the image forming apparatus 42 in combination with the color conversion in the unit 6. To do.

  When the paper correction TRC is newly generated by the generation means 13i, the profile management means 13 sets the paper correction TRC in the paper correspondence correction means 7. As a result, the paper correspondence correction unit 7 uses the paper correction TRC generated by the generation unit 13i to associate the gradation characteristics of the C, M, Y, and K basic colors of the image forming apparatus 42 with the user paper. To correct.

  In the above description, the profile in each conversion element of the color management module 3 only requires conversion parameters in one direction for conversion from the RGB or CMYK device color space to the PCS or vice versa. However, at least the paper profile includes both conversion parameters as a set, and among them, the profile for CMYK → PCS conversion is used for optimum profile selection and reproduction color error estimation, which will be described later, and for PCS → CMYK conversion. The profile is set in the PCS → CMYK conversion unit 6 of the color management module 3. Therefore, each entry of the paper profile DB 15 includes one CMYK → PCS conversion profile and a plurality of PCS → CMYK conversion profiles corresponding to the object, and selection of the optimum entry from the paper profile DB 15 and paper correction. The selection or new calculation of the TRC is performed using the CMYK → PCS conversion profile in each entry, and the obtained TRC and the optimum entry are added to the registration list of the profile management means 13 described later (if necessary). In addition to registering in association with each other, setting the PCS → CMYK conversion profile of the same entry in each PCS → CMYK conversion unit 6 that switches according to the object makes it possible to associate color conversion suitable for the object.

  Of course, as each of the above-described profiles, a profile according to the above-described ICC profile format (hereinafter referred to as an ICC profile) may be used. In particular, when an ICC profile is used as the paper profile, the ICC profile is divided into a PCS → CMYK conversion profile and a CMYK → for each of three types of rendering intents “perception”, “relative colorimetry”, and “saturation”. Since the PCS conversion profile is held, the CMYK → PCS conversion profile for relative colorimetry is used for selecting the optimum profile and estimating the reproduction color error, which will be described later.

  Next, a specific example of the user interface provided in the color image processing apparatus 41 according to the present embodiment will be described. FIG. 5 is an example of a color management setting screen displayed as a user interface on the console 18 of the color image processing apparatus 41. On this color management setting screen 20, a pull-down menu 21, a calibration execution button 22, pull-down menus 23 and 24, a setting button 25, a cancel button 26, a check box 32, and a setting sheet estimation button 33 are displayed.

  Each pull-down menu 21, 23, 24 on the color management setting screen 20 corresponds to the user interface for selecting the various DB elements in FIG. 3, the pull-down menu 21 corresponds to the paper profile DB 15, and the pull-down menu 23. 24 correspond to the simulation profile DB 14.

  Options 27 displayed when the pull-down menu 21 is pressed include an “automatic selection by calibration” 28, a registered list 29, a new / edit menu 30, and a delete menu 31. The registered list 29 is associated with the user registration area 37 of the paper registration list 35 described above. The setting sheet estimation button 33 is a button for instructing to automatically select and set a menu that is optimal for setting in the pull-down menu 21. Details of these operations will be described later. Even when the pull-down menus 23 and 24 are pressed, the registered list of the simulation profile DB 14 related to each is displayed as an option.

  When the check box 32 is checked, if there is a profile embedded in the document data 1 of FIG. 3, the settings of the pull-down menus 23 and 24 are ignored, and the embedded profile is replaced by the RGB → PCS conversion unit 4 instead. Alternatively, it is used as a setting parameter of the CMYK → PCS conversion unit 5.

  FIG. 6 shows an example of the paper profile setting screen 70 displayed when the new / edit menu 30 is selected from the options 27 of the pull-down menu 21 shown in FIG. On the paper profile setting screen 70, pull-down menus 71, 72, 73, a calibration execution button 22, a setting button 77, and a cancel button 78 are displayed.

  When the pull-down menu 71 on the paper profile setting screen 70 is pressed, a new registration menu 79 and a registered list 29 are displayed. The user selects a registered name to be edited from the already registered list 29 or selects a new registration menu 79 to register a new name in the list.

  When the pull-down menu 72 is pressed, a mode menu 80 is displayed. Each item of the mode menu 80 is associated with the gradation processing parameter set in the gradation processing means 9 registered in the gradation processing parameter DB 17 and the gradation correction data (TRC) set in the gradation correction means 8. The gradation processing unit 9 sets “gradation priority” as a tone-oriented parameter suitable for a photographic image, and “resolution priority” as a resolution-oriented parameter suitable for a character / line image. At the same time, the gradation correction data (TRC) corresponding to it is set in the gradation correction means 8. These set values are applied to the calibration chart described above that is output when calibration is executed.

  The pull-down menu 73 is a user interface for selecting and specifying a profile registered in advance in the paper profile DB 15. When the pull-down menu 73 is pressed, a paper profile selection menu 81 is displayed. When “automatic selection” is selected from the paper profile selection menu 81 by the user, it is automatically performed when calibration is executed. An optimal paper profile is selected.

  If a registered entry is selected from the registered list 29 by pressing the pull-down menu 71, the pull-down menu 72 and the pull-down menu 73 are displayed in association with the selected entry name. The When the new registration menu 79 is selected, gradation priority and automatic selection of the paper profile are selected as default values.

  The calibration execution button 22 is a user interface that the user presses to instruct execution of calibration.

  Next, a specific example of processing executed in the color image processing apparatus 41 according to the present embodiment will be described in more detail.

  FIG. 7 is a flowchart showing the flow of color management setting processing executed by the profile management means 13 in response to a user operation using the color management setting screen 20 of FIG. Note that a node 1 surrounded by a circle in the drawing represents a connection to the node 1 ', and a node 2 represents a connection to the node 2'. In FIG. 7, a loop formed by connecting the node 1 and the node 1 ′ represents a main event loop.

  When displaying the color management setting screen 20 on the console 18 of the color image processing device 41, first, in step S101, initialization of the screen according to the current setting value (if the setting value is undefined, it is determined in advance. Default values) and set values are saved.

  Next, in step S102, it is determined whether or not the setting sheet estimation button 33 is pressed on the color management setting screen 20. If the setting sheet estimation button 33 has been pressed (step S102: Yes), the process proceeds to step S103. If the setting sheet estimation button 33 has not been pressed (step S102: No), the process proceeds to step S105.

  In step S103, the registered sheet similar to the user sheet used as the image forming medium by the image forming apparatus 42 is estimated (sheet estimation process). Specifically, for example, when the paper feed stacker 94a is selected in advance by a user interface different from the color management setting screen 20, the detection value from the spectral colorimetric device 97a is acquired, and the paper feed stacker is acquired. When 94b is selected, the detection value from the spectrocolorimeter 97b is acquired. Then, based on the acquired spectral reflectance of the user paper, a score value that is a feature amount reflecting the color reproduction characteristics of the user paper is calculated. Of the plurality of already registered sheets, a sheet whose difference evaluation value with respect to the score value of the user sheet is equal to or smaller than a predetermined threshold is estimated as a registered sheet having color reproduction characteristics similar to the user sheet. . Details of this paper estimation process will be described later.

  In the next step S104, the display of the pull-down menu 21 for selecting the paper profile and the selection value are changed based on the estimated value in step S103. Here, if there is one or more registered papers that are estimated to have similar color reproduction characteristics to the user paper in step S103, the registered list 29 displayed as the option 27 of the paper profile selection pull-down menu 21 is displayed as the user paper. Therefore, it is limited to registered papers that are estimated to have similar color reproduction characteristics.

  In step S105, it is determined whether or not the paper profile selection pull-down menu 21 is pressed on the color management setting screen 20. If the paper profile selection pull-down menu 21 is pressed (step S105: Yes), the process proceeds to step S106. If the paper profile selection pull-down menu 21 is not pressed (step S105: No), the process proceeds to step S108. move on.

  In step S <b> 106, a paper profile to be set in the PCS → CMYK conversion unit 6 of the color management module 3 is selected according to the option 27 of the pull-down menu 21. When the new / edit menu 30 is selected from the options 27, the paper profile is selected after performing the editing process using the paper profile setting screen 70 shown in FIG. In addition, when the delete menu 31 is selected from the choices 27, after the entry to be deleted is selected and deleted from the registered list 29 in response to a user operation using a separately displayed selection screen (not shown). The paper profile is selected. If any other option is selected, the selected value is confirmed and the process proceeds to step S107.

  In step S107, the display of the pull-down menu 21 for selecting the paper profile and the selection value are changed according to the selection value in step S106.

  In step S108, it is determined whether or not the calibration execution button 22 has been pressed on the color management setting screen 20. If the calibration execution button 22 has been pressed (step S108: Yes), the process proceeds to step S109. If the calibration execution button 22 has not been pressed (step S108: No), the process proceeds to step S112.

  In step S109, calibration processing is executed for user paper whose color reproduction characteristics are unknown, and the process proceeds to step S110. Details of this calibration processing will be described later.

  In step S110, it is determined whether or not the paper profile set in the PCS → CMYK conversion unit 6 of the color management module 3 has been changed by the calibration process in step S109. If the paper profile has been changed (step S110: Yes), the process proceeds to step S111. If the paper profile has not been changed (step S110: No), the process proceeds to step S112.

  In step S111, the display and selection value of the pull-down menu 21 for selecting the paper profile are changed according to the result of the calibration process in step S109.

  In step S112, it is determined whether or not the RGB simulation profile selection pull-down menu 23 is pressed on the color management setting screen 20. If the RGB simulation profile selection pull-down menu 23 is pressed (step S112: Yes), the process proceeds to step S113. If the RGB simulation profile selection pull-down menu 23 is not pressed (step S112: No), step S113 is performed. The process proceeds to S115.

  In step S113, a simulation profile to be set in the RGB → PCS conversion unit 4 of the color management module 3 is selected according to the options of the pull-down menu 23, and the process proceeds to step S114.

  In step S114, the display of the pull-down menu 23 for selecting the RGB simulation profile and the selection value are changed according to the selection value in step S113.

  In step S115, it is determined whether or not the CMYK simulation profile selection pull-down menu 24 is pressed on the color management setting screen 20. If the pull-down menu 24 for selecting the CMYK simulation profile is pressed (step S115: Yes), the process proceeds to step S116, and if the pull-down menu 24 for selecting the CMYK simulation profile is not pressed (step S115: No) The process proceeds to S118.

  In step S116, the simulation profile to be set in the CMYK → PCS conversion unit 5 of the color management module 3 is selected according to the options of the pull-down menu 24, and the process proceeds to step S117.

  In step S117, the display of the pull-down menu 24 for selecting the CMYK simulation profile and the selection value are changed according to the selection value in step S116.

  In step S118, it is determined whether or not the check box 32 for instructing embedding profile priority is pressed on the color management setting screen 20. If the check box 32 is pressed (step S118: Yes), the process proceeds to step S119. If the check box 32 is not pressed (step S118: No), the process proceeds to step S120.

  In step S119, the ON / OFF display state of the check box 32 and its value are inverted (toggle operation), and the process proceeds to step S120.

  In step S120, it is determined whether or not the cancel button 26 has been pressed on the color management setting screen 20. If the cancel button 26 is pressed (step S120: Yes), the process proceeds to step S121, and if the cancel button 26 is not pressed (step S120: No), the process proceeds to step S122.

  In step S121, all the setting values saved in step S101 are restored, and the series of processes is terminated.

  In step S122, it is determined whether or not the setting button 25 has been pressed on the color management setting screen 20. If the setting button 25 is pressed (step S122: Yes), a series of processing ends while retaining the set values so far, and if the setting button 25 is not pressed (step S122: No), Returning to step S102, the subsequent processing is repeated.

  FIG. 8 is a flowchart showing details of the sheet estimation processing in step S103 of FIG.

  When the paper estimation process is started, first, in step S201, the spectral colorimetry device (eg, spectral colorimetry device 97a) corresponding to the paper feed stacker (eg, paper feed stacker 94a) selected by the image forming apparatus 42 is used. The spectral reflectance of user paper of unknown color reproduction characteristics used as an image forming medium is acquired.

  In step S202, based on the average spectral reflectance of white paper and the principal component vector obtained in advance from all possible paper types, and the spectral reflectance of the user paper acquired in step S201, the first of the user paper. Score values (s1, s2, s3), which are principal component scores up to three principal components, are calculated.

  In step S203, a threshold value θd, weight coefficients (w1, w2, w3), a candidate upper limit N, a user paper score value (s1, s2, s3) calculated in step S202, and a paper registration list 35 are determined experimentally. Using the score values (s1_i, s2_i, s3_i) of the registered sheets registered in the respective entries, the color reproduction characteristics of the registered sheets registered in the respective entries of the sheet registration list 35 are user sheets. A registered sheet similar to is extracted.

Specifically, the difference evaluation value di between the score values (s1, s2, s3) of the user paper and the score values (s1_i, s2_i, s3_i) of the registered paper is calculated using the following equation (1).
di = √w1 (s1_i−s1) ² + w2 (s2_i−s2) ² + w3 (s3_i−s3) ² (1)
Then, a maximum of N registered sheets having a score value at which the difference evaluation value di with respect to the score value of the user sheet is equal to or less than the threshold θd are extracted in ascending order of the difference evaluation value di.

  In step S204, it is determined whether or not at least one registered sheet has been extracted in step S203. If at least one registered sheet has been extracted (step S204: Yes), the display of the pull-down menu 21 for selecting a sheet profile and the selected value are used as the registered sheet (difference difference) having the minimum difference evaluation value di. If there are a plurality of registered sheets for which the evaluation value di has the minimum value, for example, priority is given to a sheet with a small registration id value), and the display of the registered list 29 of the option 27 shown in FIG. In addition to restricting to the registered sheets extracted in step (b), the registered sheets are changed to be displayed in order of increasing difference evaluation value di, and the process is terminated.

  On the other hand, if one registered sheet is not extracted in step S203 (step S204: No), a message that there is no registered sheet similar to the user sheet is displayed on the console 18 in step S205. In step S206, the selection value corresponding to the “automatic selection by calibration” 28 is designated as the selection value of the pull-down menu 21 for selecting the paper profile shown in FIG.

  In general, paper used as an image forming medium can be classified into several paper types according to the principal component score of the spectral reflectance. FIG. 9 is a diagram showing an average spectral reflectance experimentally obtained from a representative paper sample group, and FIG. 10 is a diagram showing a principal component vector of this paper sample group. In FIG. 9, the wavelength (nm) of light is represented on the horizontal axis and the spectral reflectance (%) is represented on the vertical axis. In FIG. 10, the wavelength (nm) of light is represented on the horizontal axis and the difference from the average spectral reflectance ( %) Is represented on the vertical axis. FIG. 11 shows the score distribution of the first principal component and the second principal component of the paper included in the paper sample group. The horizontal axis represents the first principal component score, and the vertical axis represents the second principal component. It is a score.

  In the example shown in FIG. 11, by dividing the first principal component score by the threshold value θ1 = 0 and the second principal component score by the threshold value θ2 = 15, the paper sample is largely divided into three sheets of A type, B type, and C type. Classified into types. These paper types show typical spectral reflection characteristics, and the same paper type has similar spectral reflection characteristics of the paper, so that the reproduction color can be reproduced within a common color gamut simply by adjusting the TRC. It is possible to approximate each other to some extent. On the other hand, since the paper spectral characteristics are greatly different between different paper types, a fundamental difference in spectral color reproduction characteristics occurs, so that the mutual approximation of reproduced colors cannot be sufficiently performed only by TRC.

  Therefore, in the color image processing apparatus 41 according to the present embodiment, when the calibration for the user paper is performed, the plurality of registered papers registered in the paper registration list 35 are processed based on the score values described above. In this way, the paper types are classified into a plurality of paper types, and it is determined which paper type the user paper belongs to. Then, a paper profile corresponding to a paper having a color reproduction characteristic closest to the colorimetric value of the calibration chart output using the user paper is registered among the registered papers classified into the same paper type as the user paper. It is selected as a paper profile to be used for color conversion when image formation is performed on paper. Here, the function of classifying a plurality of registered papers into a plurality of paper types is the classification means 13f of the profile management means 13, and the function of determining which paper type the user paper belongs to is the function of the profile management means 13. It is the determination means 13g.

  FIG. 12 is a flowchart showing details of the calibration process in step S109 of FIG.

  When the calibration process is started, first, in step S301, the above-described calibration chart is output, and guidance for urging the user to perform color measurement on the output calibration chart by the colorimetric means 12 is performed. Then, when the user performs color measurement of the calibration chart by the color measurement unit 12 according to the guidance, the color measurement value of the calibration chart is acquired from the color measurement unit 12. When the setting button 25 shown in FIG. 5 is pressed in a state where the colorimetric value is not acquired, a warning that the calibration is not performed is issued to the user, and the execution of the calibration is canceled. One of these is selected.

  In step S <b> 302, it is determined whether or not the setting value of the pull-down menu 21 for setting the paper profile is a setting value corresponding to “automatic selection by calibration” 28. When the setting value of the pull-down menu 21 for setting the paper profile is a setting value corresponding to “automatic selection by calibration” 28 (step S302: Yes), the process proceeds to step S303, and the pull-down menu for setting the paper profile. If the setting value of the menu 21 is not the setting value corresponding to “automatic selection by calibration” 28 (step S302: No), the process proceeds to step S310.

  In step S303, the score value calculated as described above based on the spectral reflectance of the user paper is used to determine which of the plurality of paper types classified in advance. Specifically, using the score values (s1, s2, s3) of the user paper and the predetermined threshold values θ1 and θ2, if s1 ≧ θ1, the A type, and if s1 <θ1 and s2 <θ2, B If the type is s1 <θ1 and s2 ≧ θ2, the paper type to which the user paper belongs is determined as C type. The processing in step S303 has the effect of reducing the search range in the next step S304 and the effect of guaranteeing a certain degree of consistency in the search results.

In step S304, a paper profile (BP _new ) having a color reproduction characteristic closest to the characteristic of the calorimetric value of the calibration chart acquired in step S301 is registered in the paper registration list 35 by a method described later. Among registered sheets, a sheet profile corresponding to a registered sheet belonging to the same sheet type as the user sheet determined in step S303 is selected. Note that the paper type of each registered paper registered in the paper registration list 35 is determined by the same method as described above using the score value associated with each registered paper in the paper registration list 35. Yes. Further, simultaneously with the selection of the base paper profile (hereinafter referred to as the base profile), the paper for each color of C, M, Y, and K that best approximates the output color reproduction characteristics in combination with the base profile (BP _new ). A correction TRC (TRC _new ) is generated, and an error evaluation value (E _new ) when the paper correction TRC (TRC _new ) is used is calculated.

If there are too many registered papers belonging to the same paper type as the user paper and it takes too much time to select the base profile (BP _new ), the above-described score value difference evaluation value di for the user paper It is effective to limit the number of candidates to be compared in preference to the one with a smaller value.

  In step S305, the profile setting value Prof. For the id and TRC, an error evaluation value E when these are used is calculated, and an entry (BPi, TRCi) where E becomes the minimum value Ei is selected.

In step S306, the error evaluation value (E _new ) calculated in step S304 is compared with the minimum value Ei of the error evaluation value when the paper profile and paper correction TRC of each entry in the paper registration list 35 are used. if _{new new} <Ei (step S306: _Yes), the flow proceeds to step _S307, if _{E new} ≧ Ei (step S306: No), the process proceeds to step S315.

In step S307, a dialog box is displayed on the console 18 asking whether to newly register a combination of the base profile (BP _new ) selected in step S304 and the generated paper correction TRC (TRC _new ). If registration is instructed (step S307: Yes), the process proceeds to step S308. If there is no new registration instruction (step S307: No), the process proceeds to step S315.

In step S308, the base profile (BP _new ) selected in step S304 is set in the PCS → CMYK conversion unit 6 of the color management module 3, and the paper correction TRC (TRC _new ) generated in step S304 is set in the paper correspondence correction means 7. Set to. In step S309, the sheet correction TRC (TRC _new ) generated in step S304 is registered in the sheet correction TRC-DB 16, and a name is given to the link to (BP _new , TRC _new ), and the above-described spectral analysis of the user sheet is performed. The score value calculated based on the reflectance is added to the paper registration list 35, and the process ends.

On the other hand, if the setting value of the pull-down menu 21 for setting the paper profile is not a setting value corresponding to “automatic selection by calibration” 28 in the previous step S302, that is, registered in the paper registration list 35. If an entry is selected, calculated in step S310, the relative sheet profiles of the selected entry (BPi), the error evaluation value sheet correction TRC to the _{(E new new)} minimize _{(TRC new new)} on the new Then, the process proceeds to step S311.

  In step S311, an error evaluation value Ei when the paper profile (BPi) and paper correction TRC (TRCi) of the selected entry is used is calculated.

In step S312, the error evaluation value (E _new ) when the paper correction TRC (TRC _new ) calculated in step S310 is used and the error when the registered paper correction TRC (TRCi) calculated in step S311 is used. The evaluation value Ei is compared. If E _new <Ei (step S312: Yes), the process proceeds to step S313. If E _new ≧ Ei (step S312: No), the process proceeds to step S315.

In step S313, a dialog box is displayed on the console 18 asking whether to newly register the paper correction TRC (TRC _new ) calculated in step S310. If the user instructs new registration (step S313: Yes). Proceeding to step S314, if there is no instruction for new registration (step S313: No), the process proceeds to step S315.

In step S314, the paper correction TRC (TRC _new ) calculated in step S310 is registered in the paper correction TRC-DB 16, and the TRCi of the selected entry (BPi, TRCi) in the paper registration list 35 is replaced with TRC _new .

  In step S315, the paper profile (BPi) of the selected entry is set in the PCS → CMYK conversion unit 6 of the color management module 3, and the paper correction TRC (TRCi) is set in the paper correspondence correction unit 7 to perform the processing. finish.

  FIG. 13 is a conceptual diagram illustrating a method for generating a sheet correction TRC that minimizes an error evaluation value with respect to a sheet characteristic for a sheet profile. Hereinafter, a specific example of a method for generating the paper correction TRC will be described in more detail with reference to FIG.

  In the calibration chart output at the time of calibration, the gradation processing means 9 and the gradation correction means 8 have a specific gradation processing parameter (screen set) as a calibration reference and corresponding gradation correction data (TRC). Are set from the gradation processing parameter DB 17. At this time, the gradation correction data (TRC) set in the gradation correction means 8 has gradation characteristics of the CMYK basic colors until the subsequent image output including the gradation correction means 8. Regardless of the gradation processing parameters set to, correction is performed so that the characteristics are generally defined in advance. In FIG. 13, cyan gradation correction data (TRC) is represented by a curve 50c, and magenta gradation correction data (TRC) is represented by a curve 50m. Since the same applies to yellow and black, illustration of gradation correction data (TRC) for yellow and black is omitted in FIG.

  The grid points 52 in the CMYK space 51 are obtained by combining tone values of six input values x = 0, 51, 102, 153, 204, and 255 for each of C, M, Y, and K channels. (In FIG. 13, for simplification of the drawing, a 5 × 5 two-dimensional lattice point is used for simplification, but it is conceptually shown. However, in actuality, 6 × 6 × 6 × 6 four-dimensional is shown. Grid points). The grid points on the Lab space 56 in the CMYK → PCS conversion 65 based on the paper profile are set as target grid points. The gradation correction data (TRC) of each color set in the gradation correction means 8 such as the curves 50c and 50m is preliminarily set for each gradation processing parameter so that the target grid points are distributed approximately evenly on the Lab space 56. Define it. Such gradation correction data (TRC) is actually C, M, Y, and K for each gradation processing parameter setting condition (usually the number of halftone lines) with respect to a standard sheet for each sheet profile. This is constructed by defining the TRC of each color so that the color difference based on the white color is linear with respect to the input gradation value.

  On the other hand, the calibration chart output at the time of the previous calibration execution is patch image data directly given as the CMYK input of the gradation correction unit 8 from the profile management unit 13 and the previous C, M, Y, K = 0, 51. , 102, 153, 204, and 255, a 6 × 6 × 6 × 6 color patch image is reproduced by the image forming apparatus 42.

  The profile management means 13 constructs a CMYK → PCS conversion model 66 on the user paper for an arbitrary CMYK input by using the relativized Lab values of these patch colorimetric values and a multiple linear interpolation operation. The CMYK → PCS conversion model 66 is a model of color reproduction characteristics after the gradation correction unit 8 in FIG. 3. However, when the reproduction color gamut 53 by the user paper is narrower than the color gamut 54 of the paper profile, The extended color gamut 55 is expanded to be wider than the paper profile color gamut 54 by extrapolation. For this expansion, a space 58 in which the input CMYK space 57 of the CMYK → PCS conversion model 66 of the user paper is represented by 8-bit integer values of each color 0 to 255 is expanded in the range of each color 0 to N (256 ≦ N <512). For a portion that extends to the CMYK space 59 and the input range of C, M, Y, and K exceeds 255, an interpolation function for an adjacent region (interpolation function applied to a CMYK value obtained by replacing a value exceeding 255 with 255) Extrapolate by diverting. Here, the extended range N is a value obtained by experimentally obtaining in advance a value that can cover the solid fluctuation range due to the sheet difference.

Next, the profile management means 13 is expanded for each element of CMYK lattice points {(c, m, y, k) | c, m, y, k = 0, 51, 102, 153, 204, 255}. For the output Lab value Lab _m (c, m, y, k) of the CMYK → PCS conversion model 66 (67) and the Lab value Lab _t of the previous target grid point set by the paper profile, ΔE ² = (Lab _m ( c ′, m ′, y ′, k) −Lab _t ) c ′, m ′, y ′ that minimizes ² is obtained, and (c ′, m ′, y ′) = (c, m, y) is obtained. Use the initial value. However, the value k of K is treated as a fixed value in order to match the degree of freedom with the Lab space.

  The corrected CMYK grid points 60 thus obtained are projected onto the C, M, and Y channels, the horizontal axis corresponds to the input grid point values {0, 51, 102, 153, 204, 255}, and the vertical axis corresponds to these. Correction curves 61c, 61m, and 61y for each color (the illustration of the correction curve 61y is omitted in FIG. 13) are obtained by performing least square fitting with a cubic polynomial function that passes through the origin as the projected correction value. . However, since these correction curves may exceed the 0 to 255 range due to the color gamut expansion, the paper correction TRCs 62c, 62m, and 62y of the 0 to 255 range (in FIG. 13) are performed by performing a relaxation process described later. The paper correction TRC 62y is not shown).

Finally, for the combination of the C, M, and Y color correction paper TRC obtained in this way and the CMYK → PCS conversion model 66 on the user paper, the Lab value (Lab _t ) of the target grid point with respect to the CMYK grid point is renewed. And an average color difference is calculated as an error evaluation value.

As the relaxation processing, for example, the correction curves 61c, 61m, and 61y of C, M, and Y are set to TRC _C , TRC _M , and TRC _Y , respectively, and x _max = max {x | TRC _C (x) ≦ 255, TRC _M (X) ≦ 255, TRC _Y (x) ≦ 255}, and values corresponding to the input values 255 of C, M, Y are TRC _C (x _max ), TRC _M (x _max ), TRC _Y ( As for x _max ), for TRC _C , a point (x ₁ , 230) where TRC _C (x ₁ ) = 230 and (255, TRC _C (x _max )) are smoothly connected with a quadratic curve. The method etc. are mentioned.

  In the above example, the input CMYK space is divided by 6 × 6 × 6 × 6 grid points. However, in order to reduce the number of colorimetric patches, it is effective to reduce the number of divisions related to K. For example, by setting the number of divided grid points to 4 only for K, the total number of patches can be 6 × 6 × 6 × 4 = 864 patches that can be sufficiently output by about one A4 size sheet. If accuracy degradation does not become a problem, it is easy to further reduce the number of CMY grid points to a smaller number of patches.

  As described above, the color reproduction characteristics according to the paper to be calibrated and the gradation processing setting condition are approximately matched with the reproduction color by the PCS → CMYK conversion in the selected paper profile. In addition, RGB → CMYK conversion obtained by combining the RGB → PCS conversion unit 4 and the PCS → CMYK conversion unit 6 of the color management module 3 shown in FIG. 3, or the CMYK → PCS conversion unit 5 and the PCS → CMYK conversion unit 6 With regard to device link type conversion such as the combined CMYK → CMYK conversion, the same system can be easily realized if there is a profile held in association with the CMYK → PCS profile in the entry of the paper profile DB 15.

  As described above in detail with specific examples, the color image processing apparatus 41 according to the present embodiment is based on the spectral reflection characteristics of user paper whose color reproduction characteristics set in the image forming apparatus 42 are unknown. Based on the calculated score value (feature value), the profile management means 13 is provided with a function for extracting a sheet that can approximate the color reproduction characteristics of the user sheet from the registered sheets registered in the registration list. Since the user interface includes a color management setting screen 20 provided with a setting sheet estimation button 33 for instructing the management means 13 to extract a sheet, color management for an image forming medium with unknown color reproduction characteristics is performed. It can be carried out simply and appropriately.

  That is, according to the color image processing apparatus 41 according to the present embodiment, the user can easily set the paper set in the paper feed stackers 94a and 94b (user paper with unknown color reproduction characteristics) according to an instruction from the user interface. Since the color reproduction characteristic type can be estimated based on the spectral reflectance obtained from the spectral colorimetry devices 97a and 97b, it is not necessary to create a profile for specifying the user paper type in advance. Thereby, the applicability to the existing profile is improved.

  Further, according to the color image processing apparatus 41 according to the present embodiment, a registered sheet that can approximate the color reproduction characteristics of the user sheet is extracted and registered in association with the registered sheet selected from among the registered sheets. Therefore, diversion of the paper profile when there is a significant color difference can be avoided. Further, since the range to which the diversion of the paper profile is applied is limited, the color gamut can be prevented from being reduced due to the diversion of the paper profile.

  Further, according to the color image processing apparatus 41 according to the present embodiment, extraction of already registered sheets (and sheet profiles) approximating the color reproduction characteristics of user sheets (thus, determination of whether or not a profile is necessary when extraction is impossible) is also possible. Including) is performed based on the feature amount calculated from the spectral reflectance directly related to the color, so that high reliability can be obtained in terms of color reproduction.

  Further, according to the color image processing apparatus 41 according to the present embodiment, when the existing profile cannot be used as it is, the user is based on the color measurement result of the calibration chart using the user paper (reproduced color by the user paper). Since a registered sheet that can best approximate the sheet is selected and a sheet correction TRC used in combination with the registered sheet is generated, a new profile can be constructed with high accuracy.

  Further, according to the color image processing apparatus 41 according to the present embodiment, the selection range when selecting a registered sheet that can best approximate the user sheet is the spectral reflection of the user sheet obtained from the spectral colorimetry devices 97a and 97b. It is limited to the range of the primary classification by the feature quantity based on the rate. The calculation method itself is also reduced to a simple feature amount comparison. Therefore, since it is not necessary to perform correlation calculation between profiles of all existing profiles and profiles corresponding to user papers, both the selection range and the determination load for selection can be reduced.

  In this embodiment, the image forming apparatus 42 is provided with spectral colorimetric devices 97a and 97b for detecting the spectral reflectance of the paper accumulated in the paper feed stackers 94a and 94b, and the color image processing device 41 performs color reproduction. When acquiring the spectral reflectance of the user paper whose characteristics are unknown, the spectral reflectance detected by the spectral colorimetric devices 97a and 97b provided in the image forming apparatus 42 is acquired. Therefore, it is not necessary for the user to perform a special operation in order to acquire the spectral reflectance of the user paper.

  Note that the above-described image processing process by the color image processing apparatus 41 according to the present embodiment is realized by the CPU of the control PC executing an image processing program installed as expansion software on the control PC. The image processing program executed by the CPU of the control PC is provided by being incorporated in advance in the ROM of the control PC, for example. The image processing program executed by the CPU of the control PC is an installable or executable file, such as a CD-ROM, a flexible disk (FD), a CD-R, a DVD (Digital Versatile Disk) or the like. The information may be provided by being recorded on a recording medium that can be read by the user. Furthermore, the image processing program executed by the CPU of the control unit PC may be stored on a computer connected to a network such as the Internet and provided by being downloaded via the network. The output control program executed by the CPU of the control unit PC may be provided or distributed via a network such as the Internet.

  The image processing program executed by the CPU of the control unit PC has a module configuration including each processing function shown in the functional block diagram of FIG. 3. By reading and executing the processing program, each processing function is loaded onto the main storage device (RAM), and each processing function is generated on the main storage device.

  Although the embodiment as an application example of the present invention has been specifically described above, the present invention is not limited to the above-described embodiment as it is, and various modifications can be made without departing from the scope of the invention in the implementation stage. And can be materialized with changes.

6 PCS → CMYK converter (color converter)
7. Paper correspondence correction means (medium correspondence correction means)
13 Profile management means (parameter management means)
20 Color management setting screen (user interface)
35 Paper Registration List (Registration List)
41 Color image processing apparatus 42 Image forming apparatus 94a, 94b Paper feed stacker (medium container)
97a, 97b Spectral colorimeter (medium sensor)

JP 2008-153810 A JP 2002-84433 A

Claims (7)

An image processing apparatus that performs image processing for unifying reproduction colors in an image forming apparatus that forms a color image on an image forming medium by superimposing a plurality of basic colors,
Based on registered color conversion parameters, a color value that depends on another device different from the image forming apparatus or a color value that does not depend on the device is displayed in a table corresponding to each basic color of the image forming apparatus. Color conversion means for converting to color values;
A registration list in which a plurality of color conversion parameters are registered in association with a plurality of image forming media having different color reproduction characteristics;
Color reproduction of the used medium among a plurality of image forming media registered in the registration list based on a feature amount calculated from a spectral reflection characteristic of the used medium that is an image forming medium set in the image forming apparatus Parameter management means having a function of extracting an image forming medium capable of approximating characteristics;
A user interface that accepts a user operation to instruct the parameter management unit to extract an image forming medium that can approximate the color reproduction characteristics of the used medium, and presents the image forming medium extracted by the parameter management unit to the user And an image processing apparatus. In the registration list, the feature amount of each image forming medium is registered in association with a plurality of registered image forming media,
The parameter management unit extracts an image forming medium having a difference evaluation value of the feature amount from the used medium that is equal to or less than a threshold value from a plurality of image forming media registered in the registration list. The image processing apparatus according to claim 1. Further comprising medium correction means for correcting the gradation characteristics of each basic color of the image forming apparatus in correspondence with the medium used based on the gradation correction parameters;
The user interface has a function of accepting a user operation for instructing start of calibration,
The parameter management unit causes the image forming apparatus to output a calibration chart in which a plurality of patch images are formed on the use medium when the user interface receives a user operation for instructing the start of calibration. Of the plurality of image forming media registered in the registration list, an image forming medium having a color reproduction characteristic closest to the characteristic of the colorimetric value obtained by measuring the calibration chart is selected, and the selected image forming medium and the use are selected. A function of generating the gradation correction parameter for correcting the difference in color reproduction characteristics with the medium by the medium-corresponding correction unit;
The color conversion parameter corresponding to the selected image forming medium is set in the color conversion unit, and the generated gradation correction parameter is set in the medium correction unit, and the color conversion parameter and the gradation correction parameter The image processing apparatus according to claim 2, wherein a combination is registered in the registration list in association with a feature amount calculated from a spectral reflection characteristic of the used medium.   The parameter management means classifies the plurality of image forming media registered in the registration list into a plurality of groups based on the feature amount of each image forming medium, and based on the feature amount of the used medium, A colorimetric value obtained by measuring the calibration chart from among the image forming media classified into the group determined to belong to the use medium by determining which of the plurality of groups the use medium belongs to The image processing apparatus according to claim 3, wherein an image forming medium having a color reproduction characteristic closest to the characteristic is selected. The image forming apparatus includes:
A medium accommodating portion for accommodating an image forming medium;
A medium sensor for detecting a spectral reflectance of the image forming medium accommodated in the medium accommodating portion,
The said parameter management means extracts the said feature-value of the said used medium from the spectral reflectance detected by the said medium sensor in the state in which the said used medium was accommodated in the said medium accommodating part. 5. The image processing device according to any one of 4 above. An image processing apparatus for unifying reproduction colors in an image forming apparatus that forms a color image on an image forming medium by superimposing a plurality of basic colors, and based on registered color conversion parameters, A color conversion unit that converts a color value that depends on another device different from the image forming apparatus or a color value that does not depend on the device into a color value corresponding to each basic color of the image forming apparatus; A registration list in which the color conversion parameters are registered in association with a plurality of image forming media having different color reproduction characteristics;
A user operation for instructing extraction of an image forming medium that can approximate the color reproduction characteristics of a used medium that is an image forming medium set in the image forming apparatus among a plurality of image forming media registered in the registration list is received. Steps,
Extracting an image forming medium capable of approximating the color reproduction characteristic of the used medium from the plurality of image forming media registered in the registration list based on the feature amount calculated from the spectral reflection characteristic of the used medium. When,
And a step of presenting the extracted image forming medium to a user. An image processing apparatus for unifying reproduction colors in an image forming apparatus that forms a color image on an image forming medium by superimposing a plurality of basic colors, and based on registered color conversion parameters, A color conversion unit that converts a color value that depends on another device different from the image forming apparatus or a color value that does not depend on the device into a color value corresponding to each basic color of the image forming apparatus; An image processing apparatus comprising: a registration list in which the color conversion parameters are registered in association with a plurality of image forming media having different color reproduction characteristics;
Color reproduction of the used medium among a plurality of image forming media registered in the registration list based on a feature amount calculated from a spectral reflection characteristic of the used medium that is an image forming medium set in the image forming apparatus An image processing program for realizing a function of extracting an image forming medium whose characteristics can be approximated.

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